What does such an anomaly imply? And what might've caused it?

[Aryan Singh]

It has stabilized now but I want to be able to understand. I am new to Space Weather; barely two-weeks since first exploring it. Geomagnetism is still something counterintuitive for me to grasp. Earlier this evening (Eastern Standard Time), I was just giddily checking space weather updates on my phone and on the magnetometers graphs page, specifically the one displaying the Magnetometer readings for the ground magnetometer at Kiruna, Sweden showed a mild -401 nT deflection equating to a G2 Geomagnetic Storm with a kp-index of 6. I am sure such occurrences happen often given that simply having metal near a magnetometer can fluctuate the readings, but I just want to understand. 

[Sam Warfel]

Quote

It has stabilized now but I want to be able to understand. I am new to Space Weather; barely two-weeks since first exploring it. Geomagnetism is still something counterintuitive for me to grasp. Earlier this evening (Eastern Standard Time), I was just giddily checking space weather updates on my phone and on the magnetometers graphs page, specifically the one displaying the Magnetometer readings for the ground magnetometer at Kiruna, Sweden showed a mild -401 nT deflection equating to a G2 Geomagnetic Storm with a kp-index of 6. I am sure such occurrences happen often given that simply having metal near a magnetometer can fluctuate the readings, but I just want to understand. 

Important thing to note here.  The k-indexes of this magnetometer are precisely that, k-indexes, not kp-indexes.  You can see over there on the side it doesn't have the p.  The p in kp stands for Planetary, so KP is Planetary KP index.  This value is calculated by averaging values from many magnetometers all around the globe.  Local "k-indexes" can be significantly higher than this average, and vary independently from it.  Since this is a northerly location, local activity is often significantly higher than elsewhere, or the average (KP).

Secondly, this magnetometer gives live data.  As you can see, the deflection spent a pretty short time in the k-6 area, and not too long in the k-5.  KP indexes are calculated and updated every three hours.  This averages out not just the many magnetometers around the globe, but also all activity in that whole time period.  So, if you have 2.8 hours of calm and .2 hours of k-6 (at many magnetometers, not just one), then the KP index will not reflect that highest value, just the average over the time period and global magnetometers.

Long story short, you can think of it as this being a local measurement that is more sensitive.  It is quite common for it to spike significantly higher than the global average.  Unless you live nearby, it doesn't mean there is necessarily high geomagnetic activity.

As to what caused this particular spike, around that time the Bz spent more time turned south.  (This is the direction of the IMF.  It must be south for geomagnetic activity and auroras to form, if it's north the solar wind simply slides off the Earth's magnetic field.)  Also, the solar wind speed was pretty high, due to an (ongoing) Coronal Hole High Speed Stream.  With this high speed solar wind, even this relatively minor and inconsistent southward orientation of the Bz was sufficient to cause some geomagnetic (auroral) activity, at the high latitude areas where this magnetometer is located.  It doesn't mean the KP index is 5 or 6, and it doesn't mean the aurora activity will extend further south.

I hope that clears it up for you!  If you have more questions don't hesitate to ask!

Edited November 22, 2021 by Orneno

[Aryan Singh]

Thanks man! Appreciate it. 

[Sam Warfel]

Happy to help!

If there's anything I missed, Sanders will probably fill it in 😁